Section 3 Fieldbus Topologies Fieldbus Topology with RS485 (PROFIBUS DP)
3BDS009029R5001 B 65
Fieldbus Topology with RS485 (PROFIBUS DP)
Bus length and speed
When a PROFIBUS network is installed, boundary conditions of the RS485 transfer
technology must be observed. The electrical network uses a shielded, twisted pair
cable. All subscribers are connected in a line-shaped bus. The transmission rate can
be adjusted in steps from 9.6 kbit/s to 1.5 Mbit/s. For extremely time-critical
PROFIBUS-DP applications, additional transmission rates of 3, 6 and 12 Mbit/s are
possible.The maximum segment length depends on the transmission rate.
Figure 20. Bus length and speed
m
10
15
100
1000
1200
10000
100
1 K 10 K 100 K 1 M 10 M
20 K
RS 232C
Transmission rate [bit/s]
RS 485
19.2 kBit/s
93.75 kBit/s
187.5 kBit/s
500 kBit/s
1500 kBit/s
12000 kBit/s
9.6 kBit/s
RS 485: PROFIBUS-DP
max. segment length
in case of copper
conductor cable
3000 kBit/s
6000 kBit/s
1000 m
400 m
200 m
100 m
1200 m
45.45 kBit/s
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